Your Cycles-rendered 3D model is stretching usually due to unapplied object scaling, flawed UV unwrapping, or distorted mesh topology.
Unapplied scaling means Cycles uses temporary transform data instead of the model’s actual size, causing distortion. Flawed UVs—like stretched islands or misalignment—make textures (and thus renders) look stretched. Distorted topology (e.g., non-manifold edges, uneven loops) can also deform the mesh during rendering.
Try applying scaling (Ctrl+A > Scale in Object Mode), checking UVs with Blender’s UV Editor Stretch tool, or inspecting for non-manifold edges (Select > Select All by Trait > Non-Manifold) to fix common issues.